Ask the Expert: Coupler & Continuity Systems

For our final ‘Ask the Expert’ of 2024 we sat down with Neil Loy, Commercial Manager for Rebar Splicing at Leviat to find out about reinforcement continuity systems and considerations for their use in infrastructure projects.

What factors should engineers consider when choosing between various reinforcement continuity options for a construction project?

When selecting a reinforcement continuity system, engineers must evaluate several performance-related factors. Strength and slip requirements are crucial, as well as considering whether fatigue will be present in the structure. Additionally, the level of accreditation required is a key consideration. In the UK, design codes such as BS 8597:2015 and BS EN 1992-1-1:2004 (EC2) apply to reinforcement couplers and continuity systems. Other factors include ease of access for installation, the environment (such as saltwater or coastal conditions), and whether projecting bars can be adapted into a coupler or continuity system connection.

What are the key considerations when selecting between hybrid couplers, reinforcement continuity systems, threaded couplers and bolted couplers for a specific infrastructure project?

The type of application is the first deciding factor. For example, if you are strengthening or extending an existing structure, a remedial system like Ancon MBT bolted couplers would be suitable. In contrast, Ancon CXL Parallel Threaded coupler systems are often more cost-effective for new construction. Performance requirements are also critical; fatigue resistance is particularly important for infrastructure projects.

What are the main advantages of using mechanical splices in reinforced concrete construction for bridges?

Mechanical splices (Rebar Couplers) offer five key benefits:

• Improved structural integrity
• No reliance on concrete for load transfer
• Reduction of rebar congestion
• Elimination of lap splice calculations
• Reduced tonnage of reinforcement (For every 1000 couplers, 14.9 tonnes of CO2 is saved¹)

Ancon Coupler Box hybrid continuity systems allow engineers the flexibility of being able to design connections without the traditional restrictions on bar length and diameter of traditional re-bend systems.

¹DEFRA - Average global CO2 for steel is 1571kgs/tonne 

How do reinforcement continuity systems contribute to the flexibility of reinforcement design in infrastructure projects?

In areas with smaller diameters of non-fatigue-prone reinforcement, continuity systems provide a cost-effective and quick to install solution. They help ensure reinforcement continuity across construction joints, particularly in wall/slab or slab/slab connections. These systems simplify formwork design, save installation time, and enhance health and safety by eliminating protruding bars, which can cause injuries.

In what scenarios might threaded or bolted couplers be preferred over other, more traditional, reinforcement connection methods in bridge construction?

Mechanical splices (rebar couplers) are a practical alternative to lap splices or welded connections, which are often challenging to implement on-site and come with stringent quality controls. Mechanical splices prevent bar protrusion at joints, reduce congestion, save rebar length and protect formwork. Unlike lapped joints, which rely on concrete bonding for load transfer, rebar couplers function like a continuous length of rebar. This is a crucial feature in seismic designs or for bridge piers vulnerable to impacts from large vehicles or ships.

How do different types of reinforcement continuity systems compare in terms of installation methods and ease of use?

There are a variety of reinforcement continuity systems available to suit different applications. Some require the fixing of individual bars, while others come with multiple bars pre-fixed into carrier cases or flexible steel strips. Anchor systems, cast-in options, and different connection methods - such as torqued (Ancon Tapered Thread Couplers), wrench-tightened (Ancon CXL Couplers), lock shear bolts (Ancon MBT Couplers), or re-straightened (Ancon Reinforcement Continuity Systems) - are all straightforward to install. The type of project typically dictates which system is best.  For example, Ancon MBT bolted couplers are more suitable for remedial work and less practical for new construction in heavily congested areas.

How do threaded couplers impact the speed and efficiency of concrete reinforcement installation in bridge construction?

When compared to overlapped joints, rebar couplers (threaded or bolted) offer the following advantages:

• Couplers reduce rebar congestion when compared to lapped joints which can compromise structural integrity of the structure.
• Degradation of concrete could affect the transfer of load with lapped joints.
• Less steel is used with coupled connections, resulting in material and cost savings.
• Cost and material efficiency results in a greener and ‘lighter’ building.
• Where used to connect starter bars, couplers help avoid damage to formwork.

Can you describe the key differences between parallel-threaded and tapered -threaded connections?

Parallel-threaded systems, while requiring significant capital investment in rebar threading equipment, meet stringent performance standards for large infrastructure projects. Tapered-threaded systems, on the other hand, require less expensive processing equipment but involve larger, more costly couplers. These systems also need calibrated torque wrenches, which can be impractical on-site. When dealing with large, heavy bars, positional couplers are required, which can be more cost-effectively achieved with parallel-threaded systems than with tapered-threaded ones.

To speak to one of our technical experts about the best product for your project, contact us by email on reinforcement.uk@leviat.com or by telephone on: +44 (0) 114 275 5224

To read the ‘Ask the Experts’ from our other product brands visit our Leviat website.